Note: Descriptions are shown in the official language in which they were submitted.
CA 02559583 1996-08-27
SPLINED VIBRATION DAMPING DEVICE USING ER FLUIDS
BACKGROUND OF THE INVENTION
Technical Field
The invention relates to vibration damping devices which develop
damping performance when being applied to a suspension member, such as for
automobiles or other equipment. More particularly, the invention relates to
such a
damping device using an electrorheological (ER) fluid as the damping medium,
which device is of a relatively simple structure, easy to assemble and to
apply a
voltage to the ER fluid contained therein for changing the damping
characteristics of
the device. Even more particularly, the invention relates to an ER damper in
which
one or both of the electrodes have a splined or fluted configuration.
Background Information
Vibration damping devices have been used for considerable periods of
time to dampen the vibrational forces applied to the suspension system of
vehicles to
provide a smoother ride by reducing the vibrations caused by road bumps and
depressions passing from the tires to the vehicle frame by the interposing of
oil-filled
shock absorbers or high-pressure gas damping devices.
Although these prior art oil and high-pressure gas damping devices
have proven satisfactory, a more recent development has evolved in which an
electrorheological or electroviscous fluid is used within the chamber of the
damping
device, wherein the liquid is in contact with one or more electrodes, usually
mounted
in a restrictive passage, which depending upon the size of the electrodes and
the
amount of voltage applied to the liquid, will change the viscosity of the
liquid,
enabling the damping device to have a greater range of damping characteristics
than
those achieved by the high-pressure gas or oil-filled shock absorbers.
An example of an anti-vibration device which uses an expandable
liquid chamber containing an electrorheological fluid is shown in U. S. Patent
No.
4,973,031. U. S. Patent No. 4,858,733 discloses another damping device using
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electrodes in combination with an electroviscous liquid contained within
closed
chambers. The liquid is movable through a restricted passage where voltage is
applied to the electroviscous liquid as it moves through the passage to change
its
viscosity to achieve various damping effects. Various other types of such ER
vibration damping devices use elastomeric members or sleeves for containing
the ER
fluid, such as shown in U. S. Patent No. 5,180,145. Although these devices
have
proved satisfactory, they are limited as to the amount of internal pressures
available
for damping, since the sleeves expand and affect the response time.
Therefore, the use of rigid fluid chambers formed of metal have been
utilized with ER fluids in order to be able to develop higher internal
pressure and
quicker response times. U. S. Patent Nos. 4,819,772 and 5,259,487 are believed
to be
the closest prior art to the vibration damping device of the present
invention. The
damping devices of both of these patents use an ER fluid which is contained
within
rigid housings to provide for increased pressures and quicker response time
not
believed obtainable with ER dampers using an elastomeric sleeve or bellows for
the
chamber-forming member.
However, the structures of both of these prior art damping devices
require a complicated structure consisting of numerous parts in order to
achieve the
electrical isolation required for applying a voltage to the restricted
orifices or ducts
through which the ER fluid moves, and requires the passage of the wires
applying the
voltage to the electrode to pass through the ER fluid chamber. Likewise, the
outer
body or housing must be of a rigid metal, since this outer housing is
connected at one
end directly to one of the spaced vehicle components, and therefore must be of
sufficient strength to support the various loads and forces applied thereto.
An outer
end of the piston rod is connected to the other of the spaced vehicle
components for
mounting the vibration damping device on the vehicle.
Another problem that can exist in dampers using ER fluids is that the
constricted areas adjacent the electrodes can cause a high shear-rate in the
restricted
flow channel, thereby decreasing the difference between field-on and field-off
damping force values provided by the ER effect. Some of these problems are
eliminated by the providing of bleed holes or check valves in the piston.
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Thus, the need exists for an improved vibration damping device using
ER fluids which is of a simpler construction, which is able to withstand the
various
loads and forces exerted thereon when mounted between spaced structural
components of a vehicle, and which enables a voltage to be applied to the
electrode
contained within the damping device in an easier manner than existing ER fluid
dampers, and which reduces the high shear-rate in the flow channel.
SUMMARY OF THE INVENTION
Objectives of the invention include providing a damping device using
ER fluids, preferably of the type adapted to be incorporated within a vehicle
suspension system, which solves the aforementioned problems of prior art
dampers
by reducing the complexity of the damper without sacrificing the damping
characteristics achieved thereby.
A still further objective of the invention is to provide such a damping
device which, when used with an electrorheological or electroviscous fluid,
enables
the orifice and associated electrode to have various configurations in order
to achieve
various damping characteristics.
Another objective of the invention is to provide such a damping
device which is of a considerably simpler structure than prior dampers using
ER
fluids, and which is able to withstand the various loads and forces exerted
thereon
when mounted between spaced components in a vehicle suspension system.
A further objective of the invention is to provide such a damping
device in which the electrode for supplying voltage to the ER fluid is mounted
outwardly of the ER fluid to eliminate the passing of the . electrical wires,
which
supplies the voltage to the electrode, through the ER fluid, as in prior
dampers using
ER fluids.
A still further objective of the invention is to provide such a damping
device which incorporates a pressurized gas reservoir within the damper to
prevent
cavitation and the formation of bubbles within the ER fluid, thereby
preventing the
creation of electrical arcing within the fluid.
Still another objective of the invention is to provide such a damper in
which the outer housing can be formed of a dielectric material, with the inner
housing
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which forms the piston chamber being formed of metal, thereby enabling smaller
diameter cylinders to be used, and to enable all metal components of the
damper
except for the electrode, to be grounded, to reduce the risk of electrical
shorts or
shocks.
A further objective of the invention is to provide a damper which
reduces the shear-rate in the flow channel by providing small bleed grooves in
the
flow channel to relieve high hydraulic pressure and to prevent harshness in
the
vehicle, and to give extra flow area to decrease shear-rate of the ER fluids
by
providing a fluted or splined electrode configuration throughout all or a part
of the
flow channel.
Another objective of the invention is to provide a damper having a
fluted or splined outer electrode and a similar-shaped inner electrode,
wherein ridges
formed on the inner electrode are positioned opposite of the valleys of the
hot or
outer electrode to form small bleed grooves in the valleys of the electrodes,
and to
provide a secondary ground electrode to provide an additional electric field
between
the peaks and flutes and the ground electrode to allow the valleys of the
flutes to be
electrified, thereby reducing the amount of electric field leakage.
Still another objective of the invention is to provide such a damping
device which can be easily assembled and disassembled for repair and ease of
manufacture without sacrificing the integrity of the device.
A further objective of the invention is to provide such an improved
damping device which is of a rugged, compact, relatively lightweight, simple
design,
which achieves the stated objectives in a simple and efficient manner.
These objectives and advantages are obtained by the vibration
damping device of the present invention, the general nature of which rnay be
stated as
including an inner housing forming a piston chamber; a piston axially movable
within
the piston chamber and dividing said chamber into two separate fluid chambers,
said
piston having a piston rod extending out of said inner housing; an outer
housing
surrounding at least a portion of the inner housing; first means for
connecting the
piston rod to a first support structure; second means for connecting one of
the
housings to a second structure spaced from the first structure, whereby load
on said
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damping device is supported by said one housing and the piston rod; fluid
transfer
duct means formed between said inner and outer housings providing fluid
communication between said fluid chambers on opposite sides of said piston,
said
fluid chambers adapted to be filled with an electrorheological (ER) fluid; and
electrode means mounted in the transfer duct means for applying an electric
field
across at least a portion of the duct means to increase the flow resistance of
the ER
fluid passing therethrough, said electrode means being formed with a plurality
of
circumferentially spaced splines and intervening grooves extending
longitudinally
throughout at least a portion of the duct means.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention, illustrative of the best modes
in which applicants have contemplated applying the principles, are set forth
in the
following description and are shown in the drawings and are particularly and
distinctly pointed out and set forth in the appended claims.
FIG. 1 is a side elevational view of the vibration damping device of
the present invention;
FIG. 2 is an enlarged fragmentary perspective view, with portions
broken away and in section, of the vibration damping device shown in FIG. 1;
FIG. 3 is an enlarged fragmentary longitudinal sectional view of the
damping device of FIG. 1;
FIG. 4 is a sectional view taken on line 4-4, FIG. 3;
FIG. 4A is a greatly enlarged fragmentary sectional view of the
encircled portion of FIG. 4; FIG. S is a sectional view taken on line S-5,
FIG. 3;
FIG. 6 is a fragmentary longitudinal sectional view similar to FIG. 3 of
a second embodiment of the vibration damping device of the present invention;
FIG. 7 is a sectional view taken on line 7-7, FIG. 6;
FIG. 8 is a sectional view taken on line 8-8, FIG. 6;
FIG. 9 is an enlarged fragmentary sectional view of the encircled
portion of FIG. 7;
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FIGS. 10 and 11 are sectional views similar to FIGS. 4-5 and 7-8,
respectively, of a third embodiment of the vibration damping device of the
present
invention; and
FIG. 12 is an enlarged fragmentary sectional view of the encircled
portion of FIG. 10.
Similar numerals refer to similar parts throughout the drawings.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A first embodiment of the improved vibration damping device is
indicated generally at 1, and is shown in FIGS. 1-5. Device 1 includes an
inner
housing 2 formed of a rigid metal having an elongated, generally cylindrical
body 3
with inner and outer cylindrical surfaces 4 and 5, respectively. One end of
cylindrical
body 3 is open at 6, with the other end being closed by a wall 7.
A piston 10 is slidably mounted within a piston chamber 11 formed
within cylindrical body 3, and has a piston rod 12 attached thereto. Rod 12
extends
through a complementary-shaped opening 13 formed in an end closure ring 14.
Ring
14 is mounted within open end 6 of cylindrical body 3, and is sealingly
engaged
therewith by an outer O-ring 15 and an inner O-ring 16. Piston rod 12 also
extends
through a complementary-shaped opening 17 formed in an end cap 18. As shown in
FIG. 1, a connector 20 is mounted on the outer end of piston rod 12 for
securing the
piston rod to a vehicle component. A usual jounce bumper 21 will be mounted on
piston rod 12 adjacent connector 20 for absorbing severe forces exerted on
vibration
damper 1 to prevent damage thereto upon the vehicle experiencing severe
depressions
or bumps in a road surface.
Damper 1 further includes an outer housing, indicated generally at 25,
which in the embodiment of FIGS. 1-5 is formed of a dielectric material, such
as
various types of high-strength plastic materials. Housing 25 preferably is
formed of
two cylindrical portions 26 and 27 which are axially telescopically joined at
their
inner ends 26a and 27a, and fluidly sealed by a pair of O-rings 28.
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The outer end of cylindrical portion 27 is secured in position on inner
housing 2 by a clip ring 29, and is sealingly engaged with the outer surface
of housing
2 by a spaced pair of O-rings 30. The outer end of cylindrical portion 26 is
also
sealingly engaged with the outer surface of inner housing 2 by a spaced pair
of O-
rings 31. Cylindrical portions 26 and 27 of outer housing 25 are slidably
mounted and
assembled on inner housing 2, and secured in an adjusted position by an
adjustment
screw ring 33 which is threadably engaged with an internally threaded portion
34 at
the outer end of cylindrical housing portion 26. Screw ring 33 is retained in
position
by a clip ring 35.
The outer diameter of inner cylindrical housing 2 is less than the inner
diameter of outer housing 25 in order to provide an annular fluid transfer
duct 37
therebetween (FIG. 3), which duct extends generally throughout the axial
length of
outer housing 25. Piston 10 divides chamber 11 into a pair of fluid chambers
38 and
39, which communicate with transfer duct 37 by a plurality of elongated slots
40
formed in cylindrical body 3 of housing 2. Thus, as shown in FIGS. 2 and 3, as
piston
10 moves within chamber 11, an electrorheological (ER) fluid which is
contained
within chamber 11 will flow through openings 40 and along transfer duct 37
between
the two fluid chambers, depending upon the direction of movement of the
piston. A
hole is formed in outer housing 25 and communicates with fluid transfer duct
37 in
order to fill piston chamber 11 and transfer duct 37 with an ER fluid. A
threaded plug
43 will seal the fill hole after filling of damper 1 with an ER fluid.
A pressure chamber 45 is formed in one end of inner housing 2 and is
separated from piston chamber 11 by an axially slidably mounted piston or
partition
wall 46 which is fluidly sealed from chamber 11 by an O-ring 47. Chamber 45
will be
filled with a pressurized compressible gas. Upon movement of piston 10 within
chamber 11, wall 46 will move into and away from chamber 45 to compensate for
the
change of volume within chamber 11 caused by the movement of piston rod 12
into
and out of the chamber. This movement of wall 46 will maintain a generally
constant
pressure within the ER fluid to prevent the formation of air bubbles or
cavitation,
which could cause electrical arcing and shorting when a voltage is applied to
the ER
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fluid, as described below. A valve 48 communicates with pressure chamber 45
for
supplying the pressurized gas into the chamber.
A connector 49 is rigidly secured by welds to end closure wall 7 of
inner housing 2 for mounting the vibration damper on another portion of a
vehicle
S spaced from that portion of the vehicle to which piston rod connector 20 is
attached.
An elastomeric bushing 50 preferably is mounted within connector 49 to assist
in
absorbing small vibrations imparted on the vehicle and damper to assist in
achieving
the desired damping characteristics.
An electrode 52 is mounted within fluid transfer duct 37 adjacent the
inner cylindrical surface of outer housing 25. Electrode 52 is a cylindrical
metal band
or sleeve having a cylindrical outer surface 53 which coincides with the
cylindrical
surface of outer housing 25. As shown in FIG. 3, electrode 52 preferably
extends
throughout the axial length of fluid transfer duct 37, although it could
occupy only
portions thereof without affecting the concept of the invention. In accordance
with
one of the features of the invention, electrode 52 is formed with a plurality
of
circumferentially spaced, longitudinally extending grooves 54 (FIGS. 4-S),
which
form longitudinally extending intervening splines 55. Each spline 55 has an
arcuate
outer surface 56 (FIG. 4A) which is spaced from outer cylindrical surface 5 of
inner
housing 2 by a distance (S) which defines a portion of transfer duct 37.
Electrode 52 is seated in an annular recess 63 formed in the inner
surface of outer housing 25 and is clamped in position by an inner edge 58 of
outer
housing cylindrical portion 27 upon the advancement of cylindrical portion 26
toward
portion 27 by adjustment screw ring 33 (FIG. 3). A voltage is supplied to
electrode 52
by an electrical connector 60, which extends through a complementary-shaped
opening 61 formed in outer housing 25, and which is connected to a voltage
source
by a wire 62. Electrode 52 is sealingly mounted within outer housing 25 by a
plurality
of O-rings 57.
In the preferred embodiment, electrode 52 will have between eight and
sixteen splines 55 formed equally circumferentially spaced, with the width (W)
(FIG.
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4A) of each groove 54 being within the range of .Smm and lmm, which is
approximately equal to the radial width of fluid transfer duct 37, indicated
at (S). The
depth of each groove 54, indicated at (D), is preferably between lmm and 3mm.
These parameters are believed to provide the most satisfactory results, but
may
change without materially affecting the concept of the invention and the
advantages
achieved thereby. It has been found that the relationship between the
circumferential
width (W) of groove 54 having a radial depth (D) and the radial spacing (S) or
width
of transfer duct 37, is defined by the formula (W/S)Z(1+D/S) ~.
It has been found that one of the advantages achieved by vibration
damping device 1, and, in particular, by the use of the fluted or splined
electrode 52,
is that the root or base of the grooves 54 provide small bleed grooves 59
throughout
the length of the fluid transfer duct, which heretofore had to be obtained by
placing
such bleed holes in the piston. These bleed grooves relieve excessively high
hydraulic
pressure, which is developed during movement of the piston, to prevent
harshness in
the vehicle ride. The bleed grooves 59 also give extra flow area to decrease
shear rate
of ER fluids. This decreased shear rate is believed to increase the ER effect,
namely,
the damping force difference between the voltage ON and OFF.
The operation of vibration damper 1 is best illustrated in FIG. 3. Upon
the vehicle experiencing a depression or protrusion in the roadway, the piston
will
move within chamber 11, forcing the ER fluid from one chamber into the other
chamber via fluid transfer duct 37. When passing through duct 37 adjacent
electrode
52 which has a voltage applied thereto, the viscosity of the ER fluid will be
changed,
depending upon the amount of voltage applied and the width of transfer duct 37
and
depth of grooves 54 to affect the damping characteristics of the damper, as is
well
known in the ER fluid damping art.
Inner housing 2, which is formed of rigid metal, and which provides
the ground electrode, and piston rod 12, are mounted on the vehicle at spaced
locations and support the weight and absorb the various forces exerted on the
damper.
This enables outer housing 25 to be formed of a dielectric lightweight,
preferably
plastic material, since it need not absorb any of the forces and loads as do
the outer
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housings or cylinders of prior art ER vibration dampers. Inner metal housing 2
will be
connected to ground, with only electrode 52 being electrified, which electrode
is
completely contained within a dielectric housing. The only external electrical
connection is electrical connector 60 and wire 62. Thus, all electrified
components
are substantially out of possible contact with individuals and/or surrounding
components of the vehicle. Likewise, as described above and shown in FIG. 3,
very
few components are required to form damper l, which is easily assembled by the
slip
joinder of the outer housing cylindrical portions over the inner metal housing
and
their clamping engagement with electrode 52 through the adjustment of screw
ring
33.
A second embodiment of the vibration damping device of the present
invention is indicated generally at 70, and is shown in FIGS. 6-9. Damper 70
is
similar in most respects to damper 1 discussed above, except that the inner
housing,
indicated generally at 71, is formed with a plurality of longitudinally or
axially
extending projections or ridges 72 (FIG. 9) which are adapted to extend into
grooves
54 of hot electrode 52. Inner housing 71 is formed of metal and includes a
cylindrical
inner surface 73 which is slidably engaged by piston 10, as discussed
previously. The
principal difference between dampers 1 and 70 is the formation of projections
72,
which are spaced equally circumferentially about the outer surface of housing
71, and
extend into grooves 54, as indicated above. This construction provides for a
more
even electric field being applied throughout the fluid transfer duct 74, in
contrast to
the less uniform electric field of damper 1. However, fluid transfer duct 74
of damper
70 does not provide the bleed grooves as does damper I discussed above.
The operation and effects achieved by damper 70 are generally similar
to that discussed above, with the exception of the elimination of the bleed
grooves. In
damper 70, the distance between projections 72 and the portions of electrode
52
which form grooves 54 is preferably constant, which also is. equal to the
radial
distance between the outer arcuate surfaces 56 of splines 55 with respect to
the
arcuate surfaces 76 formed between adjacent projections 72.
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Electrode 52, as well as inner housing 71, as in damper 1, preferably
extends throughout the axial length of fluid transfer duct 74 and provides a
uniform
continuous cross-sectional area to the fluid transfer duct. However, for
certain
applications, it may be desirable to shorten the length of outer electrode 52
and the
fluted or grooved areas provided by inner housing proj ections 72.
A third embodiment of the present invention is indicated generally at
80, the details of which are shown in FIGS. 10-12. Damper 80 is similar to
damper 1
described above, with the exception that the outer housing 81, which also is
formed
of a dielectric material, is machined or formed with a plurality of
longitudinally or
axially extending grooves 82, preferably throughout the longitudinal or axial
length
of a fluid transfer duct 83 formed between outer housing 81 and inner
cylindrical
housing 2. In this construction, the outer or hot electrode, indicated
generally at 84, is
formed by a plurality of somewhat L-shaped metal strips 85 which extend
throughout
the length of duct 83. Each strip 85 includes an arcuate leg 86 and a radially
outwardly extending leg 87. Arcuate leg 86 is mounted adjacent the inner
arcuate
surface 88 of the spline-like projections 89 formed in outer housing 81 by
grooves 82.
Radial leg 85 extends along a side wall 90 of each groove 82.
A plurality of elongated longitudinally extending metal strips 91 are
seated within a complementary-shaped recess 92 formed in each wall 93 of
groove 82
opposite strip leg 87. Strip 91 is electrically isolated from the adjacent L-
shaped
metal strip 85 and is connected to ground.
The assembly of L-shaped metal strips 85 and metal strips 91 forms a
splined or fluted electrode configuration as that provided in dampers 1 and
70, and as
with dampers 1 and 70, when voltage is applied, an electric field is formed
between
the peaks of the splines or flutes and the opposed ground electrode provided
by inner
housing 2. However, the presence of the secondary ground electrodes provided
by
metal strips 91, allows the valleys of the flutes to be electrified, thereby
reducing and
controlling the amount of leakage or bleed of the fluid through the grooves of
the
valleys, as occurs in damper 1 described above. This configuration provides
some
leakage or bleed grooves for the ER fluid, as occurs in damper 1, but provides
control
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thereof. Although grooves 82 are shown as having generally flat bottom
surfaces 95,
they can be curved as shown in grooves 54 in dampers 1 and 70, discussed above
without affecting the results achieved thereby.
Also, the number of grooves 82 and their width and depth can vary,
depending upon the particular damping characteristics desired to be achieved
by the
damper having the electrode configuration shown in FIGS. 10-12, and, in
particular,
the secondary grounded electrodes provided by strips 91, without affecting the
concept of the invention.
The voltage may be applied to L-shaped metal strips 85, which form
the hot electrode, by a variety of structures, one example of which would be
an
energized ring (not shown) mounted at one or both ends of fluid duct 83.
In summary, the various embodiments provide for a vibration damping
device intended for use with an ER fluid, which device is of a relatively
simple
construction, easy to assemble and mount on a vehicle, and in which the fluid
transfer
duct can have various configurations. Another advantage of the present
invention is
that the electrical connection to the electrode need not pass through the ER
fluid as in
prior ER dampers, and requires that only the electrode sleeve be connected to
a
source of voltage. This provides a damper less susceptible to malfunction due
to
arcing or short circuiting of the applied voltage since the inner housing
which is
formed of metal, is connected to ground, and the outer housing can be formed
of a
dielectric insulating material, requiring only passage of the electrical
connector
through the outer housing to connect the internally located and electrically
isolated
electrode sleeve to an exterior voltage supply.
Furthermore, dampers 1, 70 and 80 provide for a fluted or splined
electrode configuration which has nonannular fluid ducts in order to provide
bleed
grooves to relieve excessively high hydraulic pressure to prevent harshness in
the
vehicle ride. The bleed grooves also give extra flow area to decrease shear
rate of ER
fluids, which is believed to increase the ER damping effect. Furthermore, the
use of
secondary ground electrode strips 91 in damper 80, provides more control for
the
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bleed grooves formed in the valleys of the grooves formed between the splines
of the
electrode.
Accordingly, the vibration damping device of the present invention is
simplified, provides an effective, safe, inexpensive, and efficient device
which
achieves all the enumerated objectives, provides for eliminating difficulties
encountered with prior devices, and solves problems and obtains new results in
the
art.
In the foregoing description, certain terms have been used for brevity,
clearness and understanding; but no unnecessary limitations are to be implied
therefrom beyond the requirement of the prior art, because such terms are used
for
descriptive purposes and are intended to be broadly construed.
Moreover, the description and illustration of the invention is by way of
example, and the scope of the invention is not limited to the exact details
shown or
described.
Having now described the features, discoveries and principles of the
invention, the manner in which the improved vibration damping device is
constructed
and used, the characteristics of the construction, and the advantageous, new
and
useful results obtained; the new and useful structures, devices, elements,
arrangements, parts and combinations, are set forth in the appended claims.
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